Electromagnetic ship&#39;s log.



lu-11 SR GROSS REFERENCE vSEARCH ROQIV FIPSEQQ XR 1%2499550 C. G. SMITH L J. SLEPIAN.

ELECTROMAGNETIC SHIPS LOG.

Arrucmou min nc.2o. 1915.

1,249,530. Patented 1m 11,1917.

UNITED STATES` PATENT CFFICE.

ennuis e. simeri, or ommen, aim Josera starren, or aosroir, nssacrrosans.

MOIAGNETIC mi LOG'.

lpeoineation of Letters Patent.

Patented Dec. 11, 1917.

Application iled December i0, 1915. Serial lo. 87,821.

To all whom it may concern.'

Be it known that we, CHARLES G. Siri'rn and Josiirri SLEPLAN, citizens of the United States, residing at Cambridge, county of Middlesex, Commonwealth of Massachusetts, and Boston, county of Suolk, and Commonwealth of Massachusetts, respectively, have invented certain new and useful Improvements in Electromagnetic Ships Logs; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The resent invention relates to electromagnetic ships logs and a method of measuring the speed of a ship.

A magnet is placed on the ships bottom so that the magnetic flux passes through the sea water. The magnetic flux traveling with the ship through the water generates a difference of electric potential in the water directly proportional to the velocity of the ship. These differences of electric potential are measured and from them the speed of the ship is determined.

In the drawings which illustrate the preferred embodiment of the invention, Figure 1 is a perspective view of the inclosed magnet and electrodes, the lower face of which is exposed to the water; Fig. 2 is a longitudinal section taken on the line 2-2 of Fig. 3; Fig. 3 is a longitudinal section taken along the line 3-3 of Fig. 2; Fig. 4 is a wiring diagram of the electrical connections and also shows a section along the line 4-4 Aof Fig. 2; and Fig. 5 is a fragmentary section alon the line 4.--4 of Fig. 2 showing l the distri uton of the magnetic ux and the direction of the induced electromotive force.

In the illustrated embodiment of the invention the magnetic flux is furnished by a permanent magnet 1, having a middle pole N and two side poles S. The magnet poles are long and narrow. The magnet is arranged inthe ships bottom so that the lower face 'of the magnet is next to the water. The

magnet is insulated from the ships bottom Van the lower face of the magnet is insulated from the water by a plate ofv insulating material 2. The ends of the magnets are closed by plates 3 of non-magnetic material. In the cavities 4 and 5 between the poles of the magnet are located electrodes 6 and 7 of amalgamated zinc. The cavities around the zinc electrodes are packed with zinc sulfate 10. The cavities are lined with insulated linings 11. In the insulating plate 2 are plates or windows 12 and 13 of porous earthenware through which the water can seep to form an electrical connection betwen the sea water and the zinc electrodes 6 and 7 in the cavities 4 and 5 respectively. While porous earthenware windows 12 and 13 allow an electrical connection through them, they do prevent any considerable difusion throu h them of the zinc sulfate so that the device may be used a long time before the zinc sulfate has to be renewed. Amalgamated zinc, sunrounded by the zinc sulfate, forms a nonpolarizable electrode even though the c hemicals used may be somewhat impure, the zinc sulfate forming a concentrated solution around the metallic zinc.

The magnet is so located that the movement of the magnet throu h the water takes place in a direction aral el to the plane of the plates 6 and 7. he lines M of magnetic flux, as shown in Fig. 5, pass from the middle pole N to the side poles S forming a magnetic field which is moved through the water in a direction perpendicular to the plane of the paper in Fig. 5, the magnetic field being transverse to the direction of movement of the magnet. The movement of this magnetic lield causes a difference of potential between the points A and B in the water at the surfaces of the earthenware windows 12 and 13, the direction of the electromotive force being indicated by the lines E. Since the windows 12 and 13 are porous and conducting, and the electrodes 6 and 7 are carried along with the magnet, the elec; trodes 6 and 7 should be maintained at substantially the same potential as the points A and B, provided the electrical resistance through the porous windows between the electrodes 6 and 7 is small or the current flowing betwen the electrodes is small or zero.

In order to measure the dierence in electromotive force induced between the points A and B, the electrodes 6 and 7 are connected through wires 20md21 totheterminals of a low rea'stance 22. A direct current is maintained throu lthe resistance 22 by means of a bat Anammeter 24 6 and anadjustable resistance 25 are included in the battery circuit. The resistance 25 is adjusted to vary the current so that the potential drop across the resistance 22 )ust balances the electromotive force induced be- 10 tween the electrodes 6 and 7 by the movement of the magnetic field M through the water. A zero instrument, such as a galvanometer 26, is placed in one of the -lea'ds 20 t or 21 and the resistance 25 is adjusted until the gvanometer 26 shows no current asstween the electrodes 6 and 7. The

v ue of the resistance 22 is known and by reading the ammeter the potential dro across the resistance 22 can be compu This potential drop is equal to the electrometive orce induced between the electrodes 6- and 7 by the movement of the magnetic field M through the water. If the magnetic field is known, the induced electromotive force 26 for dilerent speeds of shi s may be computed or may b e determin and the ammeter 24 can be calibrated to directly in knots per hour. v y

By using the zero method, the eect of so variations 1n the resistance of the water and the porous windows between the electrodes 46 and 7 is eliminated as a source of error.

The electro-dynamic theo upon which the operation of the device is ased is as folmedium electromotive forces are induced in that m ium, the intensity o`f which per unit volume is proportional to the product of the velocity of the field by the component of the magnetic force perpendicular to the direcf 50 E ['vzH] 10l j where :c indicates vector or 'geometric multilcation. In a three dimensional conducting medium under a steady state of current flow caused by a volume distribution of electromotive forces, the electric potential is determined as follows: Let E be thevector impressed electromotive force per unit volume; .00 let I be the vector current density'per unit area; let R be the scalar specific resistance of the medium; andA let the -operation Eje-RI j pgosed to b e eii'ected in the vector sense. M is a vector having magnitude be su Thus Y joining the points experimentally along the under side of the m and direction. Consider any two points C and D in the medium. Draw any ath L joining these points. Integrate at eac point of the path the component of the vector E-RI which lies along the path into the --length of the path, and we get vlifes-anun vwhere da' is the element of length along the L 1in-RI) .da

taken along :any Xathdl in (tlhe water an tis Vear from the above integral that if the B fed.;

is not to be greatly reduced by the subtraction of the term A v t y lnLfn' there must be very little current iiow in the water along any path joining the points A .and B; If the magnet 1 were inlinitely'long in a direction 1'perpendicular to the plane of t the .paperin ig. 5,'it is clear from consideratlons of symmetry that no currents would flow in the water due to the motion ofthe magnet. In this case the diiference in potential between the points A and B would be given by 4. B feas.

If the magnet 1 be cf finite length, but long induced by the electromotive forces near the middleof the magnet must flow through a narrow -volume of water longitudinally et to the ends of the' magnet and would t us have a lcircuit of high resistance. For this reason,

the porous p ates of earthenware 12 and 13 throu h which the electricalconnection is established vbetween the waterA andthe electrodes 6' and 7, are' placed midway between the'ends of the magnet 1 and are madeshort with relation to the length of the magnet. The distance from the porous plates 12 and 13 to the ends of the magnets 1s suiiicient so that current paths along the under side of the magnet to the ends of the magnet have suiciently high resistance so that B fRLdS is small compared with B fai-ds is zero and the' diierence of potential between A and B is substantially that given by B fads E-RI is independentfof R and will not change with changes in the specific resistance of the sea water. This follows from the fact that I varies inversely as R, and E is independent of R.

One of the diiculties in the practical application of the ap aratus lies in the tendency of the electro es to polarize, particularly if the electromotive force the passage of the magnetic eld throu the water causes a current to flow' through the electrodes, such, for instance, as a current to actuate a volt meter. While the described precautons afgainst polarization are e'ective and are pre' erred, other means for preventing polarization may be employed, such, for example, as other chemica depolarizers, interchanging the electrodes by me,- chanical means, or by using an alternating current method. Likewise while it is preferred to use the zero method of balancing the electromotive force induced in the water against a potential drop over a resistance, nevertheless, it is within the scope of the invention to employ other ways of measuring the electromotive force generated.

While the referred embodiment of the invention has n specifically illustrated and described, it is to be understood that the pnresent invention is not limited to its illusted embodiment but may be embodied in nerated b gli 4row poles located side by 'by the ship to be moved substantially longi- -a ship relative to the water eomlrisin other constructions within the scope of the following claims:

1. An electromagnetic ships log comprising a magnet carrled by the ship to project a magnetlc field in the water transversely of the movement of the ship therethrough, the movement of which field thro h the water induces an electromotive force 1n the water, and means for measuring the electromotive force thus induced.

2. An electromagnetic ships log comprising a magnet carried by the ship and moved longitudinally thereby through the water, said magnet maintaining a ma etic eld, the movement of which throug the water induces an electromotive force in the water, and means including electrical connections with the water near the middle of the magnet poles for measuring the eletromotive force thus induced.

3. An electromagnetic ships log comprising a magnet carried by thev shi to maintain a magnetic iield in the water, the movement of which field through the water induces an electromotive force in the water, and means for measurin the electromotive force thus induced inclu electrodes exposed to the water, and means for preventing polarization of the electrodes.

4. An electromagnetic ships log comprising a magnet ha two or more poles placed side by side an moved longitudinally y the ship through the water, said magnet maintaining a magnetic eld the movement of which through the water induces an electromotive force therein, and means including electrical connections to the water at opposite sides of one ofthe magnet poles or measuring the electromotive force induced in the water by the movement of the field.

5. An electromagnetic ships lo comprising a magnet having two or more ong, narside and carried tudinally through the water, said magnet producing a magnetic field, the motion of which through the water induces an electromotive force in the water, and means for measurin the electromotive force thus induced inc uding electrodes exposed to the water on oppositevsides of one of the magnet poles and near the middle of the magnet.

6. The method of measuring the speed of moving a magnetic eld with the ough the water, and measuring the electromotive force induced in the water by the movement of the field. 4

CHARLES G. SMITH. JOSEPH SLEPIAN. 

